Java: define terms initialization, declaration and assignment

String declaration;
String initialization = "initialization";
declaration = "initialization"; //late initialization - will initialize the variable.
    // Without this, for example, in java, you will get a compile-time error if you try 
    // to use this variable.

declaration = "assignment"; // Normal assignment. 
    // Can be done any number of times for a non-final variable

assignment: throwing away the old value of a variable and replacing it with a new one

initialization: it's a special kind of assignment: the first. Before initialization objects have null value and primitive types have default values such as 0 or false. Can be done in conjunction with declaration.

declaration: a declaration states the type of a variable, along with its name. A variable can be declared only once. It is used by the compiler to help programmers avoid mistakes such as assigning string values to integer variables. Before reading or assigning a variable, that variable must have been declared.

Declaration is not to declare "value" to a variable; it's to declare the type of the variable.

Assignment is simply the storing of a value to a variable.

Initialization is the assignment of a value to a variable at the time of declaration.

These definitions also applies to fields.

int i;  // simple declaration
i = 42  // simple assignment

int[] arr = { 1, 2, 3 };
// declaration with initialization, allows special shorthand syntax for arrays

arr = { 4, 5, 6 }; // doesn't compile, special initializer syntax invalid here
arr = new int[] { 4, 5, 6 }; // simple assignment, compiles fine

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However, it should be mentioned that "initialization" also has a more relaxed definition of "the first assignment to a variable", regardless of where it happens.

int i; // local variable declaration
if (something) i = 42;
System.out.println(i);
  // compile time error: The local variable i may not have been initialized

This, however, compiles:

int i; // the following also compiles if i were declared final
if (something) i = 42;
else i = 666;
System.out.println(i);

Here i can be "initialized" from two possible locations, by simple assignments. Because of that, if i was an array, you can't use the special array initializer shorthand syntax with this construct.

So basically "initialization" has two possible definitions, depending on context:

• In its narrowest form, it's when an assignment is comboed with declaration.
  • It allows, among other things, special array shorthand initializer syntax
• More generally, it's when an assignment is first made to a variable.
  • It allows, among other things, assignments to a final variable at multiple places.
    • The compiler would do its best to ensure that exactly one of those assignments can happen, thus "initializing" the final variable

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There's also JVM-context class and instance initialization, OOP-context object initialization, etc.